504 Boltwood — Life of Radium. 



calculate the amount of radium in equilibrium with the ionium 

 contained in a preparation of this element. Thus, for example, 

 the total activity of the substances contained in solution 1 was 

 found to be equivalent to 2591 divisions per minute in the 

 electroscope. The activity of the thorium products present 

 was calculated to be equal to 30 divisions per minute, which 

 leaves 2561 divisions per minute for the activity of the ionium. 

 Now the sensitiveness of the electroscope was such that one 

 gram of pure uranium had an activity of 124 divisions per 

 minute. The activity of the ionium in equilibrium with one 

 gram of uranium would therefore be 124 X 0*35 = 43 divisions 

 per minute. From this it follows that the ionium contained 

 in solution 1 was the amount in radio-active equilibrium with 

 59*6 grams of uranium. The amount of radium in equilibrium 

 with one gram of uranium is 3*4 X 10~ 7 gram, and the amount 

 of radium in equilibrium with the ionium contained in solution 1 

 would therefore be 2*02 X 10 -5 gram. 



The amount of radium in equilibrium with the ionium pres- 

 ent in each of the first four solutions has been calculated in 

 this manner and the results are shown in Table YI. The 

 activities taken for the total material in the different solutions 

 are calculated from the activities of the specimen films pre- 

 pared from these solutions and are expressed in terms of 

 divisions per minute in the electroscope. _At the time that 

 these values were obtained the films were about four months 

 old and had attained an essentially constant activity.* Column 

 I gives the total activity of the substances contained in the 

 solution; column II the activity clue to the thorium products 

 present; column III the activity of the ionium; qplumn IY 

 the calculated amount of uranium (in grams) with which the 

 ionium would be in radio-active equilibrium ; column Y the 

 calculated amount of radium (in gramXlO -5 ) in equilibrium 

 with the ionium ; column YI the observed growth of radium 

 per year in terms of gramXlO -9 ; column YII the fraction of 

 the radium undergoing change per year as given by the ratio 

 of the amount of radium produced to the amount in equi- 

 librium with the ionium. 











Table 



VI 







Sol. 

 No. 



I 



II 



III 



IY 



V 



VI 



VII 



1 



2591 



30 



2561 



59-6 



2-02 



6-90 



3-41X10' 



2 



3485 



84 



3401 



79-1 



2-69 



9 01 



3-35X10 



3 



4495 



90 



4405 



102-4 



3-48 



12-45 



3-57X10 



4 



1268 



68 



1200 



28-0 



0-95 



3-19 



3-35X 10 



*The activity of these films will probably fall slowly with the time owing 

 to the decay of the radiothorium contained in them. 



